Hinkley Point C fish tunnel breakthrough: hydraulic and marine design notes for engineers
Reviewed by Tom Sullivan
First reported on The Construction Index
30 Second Briefing
Completion of the 620m fish return tunnel at Hinkley Point C marks seabed breakthrough for the final section of 8km of marine tunnels under the Bristol Channel. The tunnel boring machine, launched from dry land and recovered offshore by floating crane after a five‑month drive, will be cleaned and redeployed on another site. The tunnel will work with an acoustic fish deterrent and four low‑speed seawater intakes designed so fish can escape even when within about 2m of the intake heads.
Technical Brief
- Seabed breakthrough of the fish return tunnel completes a total of 8 km of marine tunnels.
- TBM is being demobilised for cleaning and reuse, indicating design for multi-project tunnelling campaigns.
Our Take
The 620 m fish return tunnel at Hinkley Point C adds to an already extensive 8 km marine tunnel network, signalling that UK nuclear coastal intakes are now being engineered with much more complex subsea layouts than earlier generations of plants.
With Hinkley Point C already under scrutiny on environmental disclosure, as flagged in the 8 September 2026 tribunal-appeal piece, the performance of this fish protection system in the Bristol Channel is likely to become a test case for future UK marine intake permitting on large infrastructure schemes.
Sizewell C’s plan to reuse the former Hinkley Point C tunnel segment facility at Avonmouth suggests that design and construction lessons from Hinkley’s marine and fish tunnels will be directly recycled into the next UK nuclear project, shortening learning curves for similar sustainability-driven features.
Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.
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